Adipose tissue-derived free fatty acids initiate myeloid cell accumulation in mouse liver in states of lipid oversupply

Impact of Short-Term Lipid Overload on Whole-Body Physiology

Complex metabolic diseases due to overnutrition such as obesity, type 2 diabetes, and fatty liver disease are a major burden on the healthcare system worldwide. Current research primarily focuses on disease endpoints and trying to understand underlying mechanisms at relatively late stages of the diseases, when irreversible damage is already done. However, complex interactions between physiological systems during disease development create a problem regarding how to build cause-and-effect relationships. Therefore, it is essential to understand the early pathophysiological effects of overnutrition, which can help us understand the origin of the disease and to design better treatment strategies. Here, we focus on early metabolic events in response to high-fat diets (HFD) in rodents. Interestingly, insulin resistance, fatty liver, and obesity-promoting systemic inflammatory responses are evident within a week when mice are given consecutive HFD meals. However, as shown in human studies, these effects are usually not visible after a single meal. Overall, these results suggest that sustained HFD-intake within days can create a hyperlipidemic environment, globally remodeling metabolism in all affected organs and resembling some of the important disease features.

Loss of adipose ATF3 promotes adipose tissue lipolysis and the development of MASH

The crosstalk between adipose tissue and the liver is finely controlled to maintain metabolic health. Yet, how adipose tissue controls toxic free fatty acid overflow into the liver remains incompletely understood. Here, we show that adipocyte activating transcription factor 3 (ATF3) was induced in human or mouse obesity. Adipocyte Atf3-/- (Atf3Adi-/-) mice developed obesity, glucose intolerance, and metabolic dysfunction-associated steatohepatitis (MASH) in chow diet, high-fat diet, or Western diet-fed mice. Blocking fatty acid flux by inhibiting hepatocyte CD36, but not the restoration of hepatic AMPK signaling, prevented the aggravation of MASH in Atf3Adi-/- mice. Further studies show that the loss of adipocyte ATF3 increased lipolysis via inducing adipose triglyceride lipase, which in turn induced lipogenesis and inflammation in hepatocytes. Moreover, Atf3Adi-/- mice had reduced energy expenditure and increased adipose lipogenesis and inflammation. Our data demonstrate that adipocyte ATF3 is a gatekeeper in counteracting MASH development under physiological and pathological conditions.

Widely targeted quantitative lipidomics reveal lipid remodeling in adipose tissue after long term of the combined exposure to bisphenol A and fructose

Adipose tissue is the main organ that stores lipids and it plays important roles in metabolic balance in the body. We recently reported in Human and Experimental Toxicology that the combined exposure to BPA and fructose may interfere with energy metabolism of adipose tissue. However, it is still unclear whether the combined exposure to BPA and fructose has the possibility to induce lipid remodeling in adipose tissue. In the present study, we performed a widely targeted quantitative lipidomic analysis of the adipose tissue of rats after 6 months of BPA and fructose combined exposure. We totally determined 734 lipid molecules in the adipose tissue of rats. Principal component analysis (PCA) showed the group of the combined exposure to higher-dose (25 μg/kg every other day) BPA and fructose can be distinguished from the groups of control, higher-dose BPA exposure and fructose exposure clearly. Partial least squares-discriminant analysis (PLS-DA) and univariate statistical analysis displayed lipids of PC(18:0_ 20:3), TG(8:0_14:0_16:0), TG(12:0_14:0_16:1), TG(10:0_16:0_16:1), TG(12:0_ 14:0_18:1), TG(14:0_ 16:0_16:1), TG(14:0_14:1_16:1), TG(8:0_ 16:1_16:2), TG(14:1_16:1_ 16:1), TG(16:1_18:1_18:1), TG(16:0_16:1_20:4) and TG(15:0_18:1_ 24:1) may contributed the most to the discrimination. These findings indicated that combined exposure to BPA and fructose has the potential to cause lipid remodeling in adipose tissue.

Quinoa Ameliorates Hepatic Steatosis, Oxidative Stress, Inflammation and Regulates the Gut Microbiota in Nonalcoholic Fatty Liver Disease Rats

A long-term high-fat diet causes hepatic steatosis, which further leads to oxidative stress and inflammation. In this study, we firstly investigated the regulation effects of different amounts of quinoa on hepatic steatosis, oxidative stress, and inflammation of rats fed a high-fat diet, then the gut microbiota was dynamically determined. Sprague-Dawley (SD, male) rats were randomized into four groups: normal controls (NC, fed standard chow), model groups (HF, fed a high-fat diet), low quinoa intake (HF + LQ), and high quinoa intake (HF + HQ) groups, which were supplemented with 9% and 27% quinoa in the high-fat feed (equivalent to 100 g/day and 300 g/day human intake, respectively). The results showed that quinoa intake significantly inhibited the hepatomegaly and splenomegaly, ameliorated hepatic steatosis pathologically; effectively rescued the decrease in the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) and the increase in malondialdehyde (MDA). The levels of tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), transforming growth factor-β (TGF-β), and leptin in rats of two quinoa groups were close to those of the NC group. Besides, high quinoa intake significantly increased the relative abundance of Akkermansia, and low quinoa intake significantly increased the relative abundance of Blautia at the genus level. The relative abundances of Blautia and Dorea in rats in the HF + HQ group were lower than those in rats in the HF + LQ group. In addition, the relative abundances of Clostridium and Turicibacter of rats in the two quinoa intervention groups were lower than those of rats in the HF group after 12 weeks of intervention. In summary, quinoa exhibits a series of beneficial effects in the prevention of nonalcoholic fatty liver disease (NAFLD) and is suggested to be a component of a daily diet for the prevention of NAFLD.

Dual roles of B lymphocytes in mouse models of diet-induced nonalcoholic fatty liver disease

BACKGROUND AND AIMS

Growing evidence suggests an important role of B cells in the development of NAFLD. However, a detailed functional analysis of B cell subsets in NAFLD pathogenesis is lacking.

APPROACH AND RESULTS

In wild-type mice, 21 weeks of high fat diet (HFD) feeding resulted in NAFLD with massive macrovesicular steatosis, modest hepatic and adipose tissue inflammation, insulin resistance, and incipient fibrosis. Remarkably, Bnull (JHT) mice were partially protected whereas B cell harboring but antibody-deficient IgMi mice were completely protected from the development of hepatic steatosis, inflammation, and fibrosis. The common feature of JHT and IgMi mice is that they do not secrete antibodies, whereas HFD feeding in wild-type mice led to increased levels of serum IgG2c. Whereas JHT mice have no B cells at all, regulatory B cells were found in the liver of both wild-type and IgMi mice. HFD reduced the number of regulatory B cells and IL-10 production in the liver of wild-type mice, whereas these increased in IgMi mice. Livers of patients with advanced liver fibrosis showed abundant deposition of IgG and stromal B cells and low numbers of IL-10 expressing cells, compatible with our experimental data.

CONCLUSIONS

B lymphocytes have both detrimental and protective effects in HFD-induced NAFLD. The lack of secreted pathogenic antibodies protects partially from NAFLD, whereas the presence of certain B cell subsets provides additional protection. IL-10-producing regulatory B cells may represent such a protective B cell subset.

PDIA3 epitope-driven immune autoreactivity contributes to hepatic damage in type 2 diabetes

A diet rich in saturated fat and carbohydrates causes low-grade chronic inflammation in several organs, including the liver, ultimately driving nonalcoholic steatohepatitis. In this setting, environment-driven lipotoxicity and glucotoxicity induce liver damage, which promotes dendritic cell activation and generates a major histocompatibility complex class II (MHC-II) immunopeptidome enriched with peptides derived from proteins involved in cellular metabolism, oxidative phosphorylation, and the stress responses. Here, we demonstrated that lipotoxicity and glucotoxicity, as driven by a high-fat and high-fructose (HFHF) diet, promoted MHC-II presentation of nested T and B cell epitopes from protein disulfide isomerase family A member 3 (PDIA3), which is involved in immunogenic cell death. Increased MHC-II presentation of PDIA3 peptides was associated with antigen-specific proliferation of hepatic CD4⁺ immune infiltrates and isotype switch of anti-PDIA3 antibodies from IgM to IgG3, indicative of cellular and humoral PDIA3 autoreactivity. Passive transfer of PDIA3-specific T cells or PDIA3-specific antibodies also exacerbated hepatocyte death, as determined by increased hepatic transaminases detected in the sera of mice subjected to an HFHF but not control diet. Increased humoral responses to PDIA3 were also observed in patients with chronic inflammatory liver conditions, including autoimmune hepatitis, primary biliary cholangitis, and type 2 diabetes. Together, our data indicated that metabolic insults caused by an HFHF diet elicited liver damage and promoted pathogenic immune autoreactivity driven by T and B cell PDIA3 epitopes.

The major urinary protein gene cluster knockout mouse as a novel model for translational metabolism research

Scientific evidence suggests that not only murine scent communication is regulated by major urinary proteins, but that their expression may also vary in response to metabolism via a yet unknown mechanism. Major urinary proteins are expressed mainly in the liver, showing a sexually dimorphic pattern with substantially higher expression in males. Here, we investigate the metabolic implications of a major urinary protein knockout in twelve-week-old male and female C57BL/6N mice during ad libitum feeding. Despite both sexes of major urinary protein knockout mice displayed numerically increased body weight and visceral adipose tissue proportions compared to sex-matched wildtype mice, the main genotype-specific metabolic differences were observed exclusively in males. Male major urinary protein knockout mice exhibited plasma and hepatic lipid accumulation accompanied by a hepatic transcriptome indicating an activation of lipogenesis. These findings match the higher major urinary protein expression in male compared to female wildtype mice, suggesting a more distinct reduction in energy requirements in male compared to female major urinary protein knockout mice. The observed sex-specific anabolic phenotype confirms a role of major urinary protein in metabolism and, since major urinary proteins are not expressed in humans, suggests the major urinary protein knockout mouse as a potential alternative model for translational metabolism research which needs to be further elucidated.

The interplay of immunology and cachexia in infection and cancer

Diverse inflammatory diseases, infections and malignancies are associated with wasting syndromes. In many of these conditions, the standards for diagnosis and treatment are lacking due to our limited understanding of the causative molecular mechanisms. Here, we discuss the complex immunological context of cachexia, a systemic catabolic syndrome that depletes both fat and muscle mass with profound consequences for patient prognosis. We highlight the main cytokine and immune cell-driven pathways that have been linked to weight loss and tissue wasting in the context of cancer-associated and infection-associated cachexia. Moreover, we discuss the potential immunometabolic consequences of cachexia on the basis of newly identified pathways and explore the multilayered area of immunometabolic crosstalk both upstream and downstream of tissue catabolism. Collectively, this Review highlights the intricate relationship of the immune system with cachexia in the context of malignant and infectious diseases.

Long Chain Fatty Acids as Modulators of Immune Cells Function: Contribution of FFA1 and FFA4 Receptors

Long-chain fatty acids are molecules that act as metabolic intermediates and constituents of membranes; however, their novel role as signaling molecules in immune function has also been demonstrated. The presence of free fatty acid (FFA) receptors on immune cells has contributed to the understanding of this new role of long-chain fatty acids (LCFAs) in immune function, showing their role as anti-inflammatory or pro-inflammatory molecules and elucidating their intracellular mechanisms. The FFA1 and FFA4 receptors, also known as GPR40 and GPR120, respectively, have been described in macrophages and neutrophils, two key cells mediating innate immune response. Ligands of the FFA1 and FFA4 receptors induce the release of a myriad of cytokines through well-defined intracellular signaling pathways. In this review, we discuss the cellular responses and intracellular mechanisms activated by LCFAs, such as oleic acid, linoleic acid, palmitic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), in T-cells, macrophages, and neutrophils, as well as the role of the FFA1 and FFA4 receptors in immune cells.

Hepatic Dendritic Cells in the Development and Progression of Metabolic Steatohepatitis

Metabolic Associated Fatty liver disease (MAFLD) is a global health problem and represents the most common cause of chronic liver disease in the world. MAFLD spectrum goes from simple steatosis to cirrhosis, in between metabolic steatohepatitis with progressive fibrosis, which pathogenesis is not completely understood. Hence, the role of the immune system has become an important fact in the trigger of inflammatory cascades in metabolic steatohepatitis and in the activation of hepatic stellate cells (HSCs). Among, the more studied immune cells in the pathogenesis of MAFLD are macrophages, T cells, natural killer and dendritic cells. In particular, hepatic dendritic cells had recently attracted a special attention, with a dual role in the pathogenesis of MAFLD. These cells have the capacity to switch from a tolerant state to active state inducing an inflammatory cascade. Furthermore, these cells play a role in the lipid storage within the liver, having, thus providing a crucial nexus between inflammation and lipid metabolism. In this review, we will discuss the current knowledge on the dual role of dendritic cells in lipid accumulation, as wells as in the triggering of hepatic inflammation and hepatocytes cell death in metabolic steatohepatitis.

Protective Effects of Methoxsalen Supplementation on Chronic Alcohol-Induced Osteopenia and Steatosis in Rats

Osteopenia or osteoporosis occurs frequently in alcoholics and patients with alcoholic fatty liver disease. Methoxsalen (MTS), 8-methoxypsoralen, improved osteoporosis in ovariectomized and diabetic mouse models; however, its effects on alcohol-induced osteopenia and steatosis have not been reported. This study examined the effects of MTS on alcohol-induced bone loss and steatosis. Rats in the alcohol groups were fed a Liber-DeCarli liquid diet containing 36% of its calories as alcohol. MTS was at 0.005% in their diet, while alendronate (positive control; 500 μg/kg BW/day) was administered orally for eight weeks. The pair-fed group received the same volume of isocaloric liquid diet containing dextrin-maltose instead of alcohol as the alcohol control group consumed the previous day. In the alcohol-fed rats, the MTS and alendronate increased the bone volume density, bone surface density and trabecular number, while the bone specific surface, trabecular separation and structure model index were decreased in the tibia. MTS down-regulated tibial tartrate-resistant acid phosphatase 5 (TRAP) expression compared to the alcohol control group. MTS or alendronate prevented chronic alcohol-induced hepatic lipid accumulation and the triglyceride level in the alcohol-fed rats by decreasing the lipogenic enzyme activities and increasing the fatty acid oxidation enzyme activities. MTS reduced significantly the serum levels of alcohol, TRAP and tumor necrosis factor-α compared to the alcohol control group. Overall, these results suggest that MTS is likely to be an alternative agent for alcoholic osteopenia and hepatosteatosis.

Liver DCs in health and disease

Hepatic dendritic cells represent a unique and multifaceted subset of antigen-presenting leukocytes that orchestrate specified immune responses in the liver. They are constantly exposed to antigens and signals derived not only from the hepatic microenvironment and the systemic circulation but also from the portal vein draining the gut and conveying food antigens as well as microbial compounds. Modulated by these various factors they shape intrahepatic immune responses during acute and chronic liver diseases, hepatocellular carcinoma and allograft tolerance as well as systemic responses to gut-derived components. Hence, hepatic DC are central targets to decipher and fine-tune innate and adaptive hepatic immune responses as well as tolerance. This review focuses on the origin of hepatic DC, the different DC subsets present in the liver and their functionality during different acute and chronic liver diseases in mice and men and will discuss potential DC directed therapeutic interventions in liver disease.

RAGE is a Potential Cause of Onset and Progression of Nonalcoholic Fatty Liver Disease

OBJECTIVE

Fatty liver is a rising global health concern, significantly increasing the burden of health care cost. Nonalcoholic fatty liver disease (NAFLD) has a correlation with metabolic syndrome and its complications.

METHOD

We reviewed the literature regarding the mechanisms of developing NAFLD through AGE-RAGE signaling.

RESULTS

NAFLD, metabolic syndrome, and production of advanced glycation end-products (AGEs) share many common risk factors and appear to be connected. AGE induces production of the receptor for AGE (RAGE). AGE-RAGE interaction contributes to fat accumulation in the liver leading to inflammation, fibrosis, insulin resistance, and other complications of the fatty liver disease. The immune system, especially macrophages, has an important defense mechanism against RAGE pathway activities.

CONCLUSION

Soluble form of RAGE (sRAGE) has the capability to reduce inflammation by blocking the interaction of AGE with RAGE. However, sRAGE has some limitations, and the best method of usage is probably autotransplantation of transfected stem cells or monocytes, as a precursor of macrophages and Kupffer cells, with a virus that carries sRAGE to alleviate the harmful effects of AGE-RAGE signaling in the settings of fatty liver disease.